This is the usual design of many of the ATM exchanges that have become known so far. Reference is made to Section 3, headed "Vermittlungsablauf", on pages 6 to 9 of an article by W. Schmidt in "Der Fernmelde=Ingenieur", No. 9, Sep. 1987, where the basic switching sequence in an ATM exchange of such a design is described.
Path information can be both connection numbers (Virtual Channel Identifiers, VCI), which are evaluated in each switching element with the aid of connection tables, and a number of addresses (routing tags) with which the individual switching elements are directly controlled. Examples of this are known in the art.
During the establishment of a call through a switching network, the path is selected on the basis of the instantaneous loading of the switching network and maintained for the whole duration of the call. It may happen that all paths that are possible for a new connection are already so heavily loaded that the new connection cannot be accepted. In many of those cases, however, one of the existing connections preventing the new connection can be routed along an alternative path through the switching network which is still sufficiently loadable. This problem also arises in conventional exchanges. The problem of eliminating local blocking by rearranging existing connections has not been satisfactorily solved because of errors occurring during the rearranging process.